Window for X-ray tubes



e 1943- Z. J. ATLEE ET AL 2,309,566

WINDOW FOR X-RAY TUBES Filed Sept. 9, 1940 INVENTORS Zed JA 6 Lee I any:

Patented Jan. 26, 1943 WINDOW FOR X-RAY TUBES Zed J. Atlee, Elmhurst, and Robert F. Wilson, Chicago, 111., assignors to General Electric X-Ray Corporation, Chicago, 111., a corporation of New York Application September 9, 1940, Serial No. 355,983

Claims.

Our invention relates in general to X-ray apparatus and has more particular reference to a" low absorption window through which X-rays generated by the operation of the tube may be trans mitted.

An important object of the invention is to provide a window subtending a relatively wide angle with respect to the source of X-rays; a further the walls to permit the window to subtend a relatively large angle of the order of 120 degrees at the center of the anode.

" Another important object is .to provide a wide angle window in X-ray apparatus of the char' acter mentioned, thereby allowing the tube to be used in an enclosing casing having a plurality of ports through any one or all of which usable X-rays may be projected for use.

The foregoing and numerous other important objects, advantages and inherent functions of the invention will become apparent as the same is more fully understood from the following description, which, taken in connection with the accompanying drawing, discloses a preferred embodiment of the invention.

Referring to the drawing:

Figur 1 is a sectional View taken longitudinally through an X-ray tube embodying our present invention;

Figure 2 is an enlarged sectional view of the anode shown in Figure 1;

Figure 3 is a side view of the anode illustrated in Figure 2, showing ,the wide angle window; and

Figure 4 is a sectional view taken substantially along the line 44 in Figure 3, showing the value of the wide angle window construction in serving a plurality of treatment ports.

To illustrate our invention, we have shown on the drawing an X-ray tube comprising a preferably cylindrical glass envelope ll having an anode l3 and a cathode l5 disposed therein in facing relationship, the anode and cathode preferably being mounted at the opposite ends of the envelope. The anode comprises a preferably cylindrical sleeve-like element I! formed of suitable material, such as copper or a cupric alloy, the sleeve-like element being provided with an'inclined wall I9 adjacent one end and defining a chamber 2| and a pocket 23 opening at the opposite ends of the anode, the pocket 23 being in axial alignment with and facing toward the cathode [5. The inclined wall I9 supports a preferably tungsten button or target 20 on the side thereof defining .the bottom of the pocket 23 in position to receive electrons emitted by the cathode l5 during the operation of the tube for the production of X-rays.

X-rays, of course, are produced at the target as a result of impingement thereon of electrons emitted by the cathode, and the walls forming the pocket 23 serve as a screen preventing electrons from escaping outwardly of the anode and impinging upon the envelope ll. Impingement of stray electrons on the envelope is undesirable because of the resulting electrical strain on the envelope and deterioration of the envelope material itself under electronic bombardment.

The end of the anode at the open end of the chamber is formed preferably with a shoulder 25 on which is sealed, as by welding or brazing, an annular sleeve 21, the end of which forms a glassto-metal seal 29, with the end of a cylindrical re-entrant portion 3| comprising an integral portion of the envelope l I at the anode end thereof. A cooling coil 33, having connecting duct portions 35 extending within the re-entrant envelope portions 3| and outwardly thereof for connection with a fluid circulating system, is secured in the chamber 2! upon the inclined wall l9, so that by circulating a cooling fluid through the coil 33, the anode, and particularly the wall I9, may be cooled, it being understood, of course, that the tube, when in operation, generates appreciable heat, particularly at the wall 19.

The walls of the anode defining the pocket 23 form a substantial X-ray screen and, in order to improve the efficiency of the device as a source of useful X-rays, the cylindrical anode wall defining the pocket 23 is cut away, as at 31, to define a window opening facing the inclined target 20 and affording an unhampered exit through which X-rays may freely pass outwardly of the anode. To prevent the escape of electrons through the opening 31, however, it is closed by a windowpane 43 of material, such as graphite or beryllium, which is substantially transparent to X- rays. To this end, the outer surfaces of the anode walls are formed with an outwardly opening marginal seat 39 at the edges of the opening 31. This seat, since the walls of the anode are cylindrical, will have curved sides 4| (Fig. 4) centering on the axis of the anode and carries the window-pane 43 which is curved in a plane having a radius of curvature equa1 to the radius of curvature of the curved sides M of the seat 39. The window is held in place by means of a clamp or frame 45 at the marginal edges of the Window in position fitting into the seat 39 and being held in place in any preferred fashion, as by means of the fastening screws 41, which extend through the frame 45 and the edges of the pane 43 and tak into the anode. It will be noted that the opening 31 subtends a relatively wide angle of the order of 120 degrees with respect to the center of the focal spot 49 of the target 20, said focal spot, of course, being the area of the target upon which the majority of the electrons emitted by the cathod impinge.

The wide angle window structure of the present invention is made possible by utilizing a curved pane and mounting it as close as possible to the target 20. The wide angle window allows the tube to transmit X-rays from the target within an angular field 5i bounded only by the separation of the edges of the opening 31 which extend parallel with respect to the axis of the anode. This wide angle field enables the tube to be placed in a casing or housing 53 having several windows 55 through each and all of which useful beams 51 of X-rays may be transmitted in different angular directions, thus greatly increasing the value of the apparatus for diagnostic and therapeutic purposes over equipment affording only one useful X-ray beam.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its attendant advantages, the form herein disclosed being a preferred embodiment for the purpose of illustrating the invention.

The invention is hereby claimed as follows:

1. The combination, with X-ray apparatus comprising an anode target aifording a source of X-rays when under electron bombardment and a screen enclosing said target against the escape of electrons, of window means on said screen comprising a pane of material having a low coefficient of X-ray absorption and curved on a radius centering at said source, said curved .pane of material subtending an angle of the order of 120 degrees with respect to the center of said source.

2. The combination, with X-ray apparatus comprising an anode target affording a source of X-rays when under electron bombardment and a screen enclosing said target against the escape of electrons, of window means on said screen comprising a pane of material having a low coefficient of X-ray absorption, said window subtending an angle of the order of degrees with respect to said source and being curved on a radius centering at said source.

3. The combination, with X-ray apparatus including an anode having a target affording a source of X-rays when excited by electron bombardment, of cylindrical walls encircling said target to prevent escape of electrons outwardly of said anode, said walls being formed opposite said target with an opening subtending an angle with respect to said target of the order of 120 degrees, and window-pane means of material having a, low coefficient of X-ray absorption secured in said opening, said window-pane means being curved in conformity with the curvature of said cylindrical walls.

4. The combination, with X-ray apparatus comprising a sealed envelope, an anode target affording a source of X-rays when under electron bombardment in said envelope, and a screen of cupric material enclosing said target against the escape of electrons from the anode to prevent electron impingement on said envelope, of window means in said screen opposite said target comprising a pane of material having a lower coefiicient of absorption than the coefficient of absorption of the material of said screen, said screen being formed with a window opening providing a curved seat subtending an angle with respect to said target of the order of 120 and said pane being correspondingly curved on a radius centering at said source and being secured in said seat.

5. The combination, with X-ray apparatus comprising an anode target affording a source of X-rays when under electron bombardment and a cylindrical screen enclosing said target against the escape of electrons, of window means on said screen comprising a pane of material having a low coefficient of X-ray absorption, said windowpane being curved on a radius centering at said source and subtending an angle of the order of 120 with respect to the center of said source whereby to provide a wide angle beam of X-rays from said source through said window when said apparatus is in operation, and a shield of material relatively impervious to X-rays surrounding said screen and window, said shield having a plurality of openings angularly spaced apartwith respect to said source and lying within the effective wide angle beam of X-rays transmitted through said window to provide a plurality of usable X-ray beams emanating from said source at relatively widely divergent angles.

ZED J. ATLEE. ROBERT F. WILSON. 

